Color comparator

ABSTRACT

A color comparator providing, in a single device, an expedient and accurate combination of filter media arranged in a generally planar relationship to provide a three dimensional effect portraying the interrelationship of the filter media. The comparator includes neutral density material for providing substantially uniform white light transmission over the entire comparator area and means to facilitate assembly.

United States Patent 1 [111 I 3,748,045

Mitchell a [45] July 24', 1973 I 1 COLOR COMPARATOR [76] lnventor:Robert w. Mitchell, 707 Myrtle 'f' Ave St Joseph, Mich- 49085 AssistantExammer-F. L. Evans Attorney-Pendleton, Neuman, Williams & Anderson [22]Filed: Apr. 19, 1971 [21] Appl. No.: 134,964

57 ABSTRACT [52] US. Cl 356/191, 355/32, 355/88 [51] Int. Cl. Gfllj 3/52A color com 1 parator provldlng, m a slngle device, an ex- [58] newofsearch 6/ l9] |95 355/32 88 pedient and accurate combination of filtermedia ar- 7 ranged in a generally planar relationship to provide a [56]References Cited three dimensional effect portraying the interrela-UNITED STATES PATENTS tionship of the filter media. The comparatorincludes 1,769,777 7/1930 Feinberg 356/192 X neutral density materialfor providing substantially uni- 2,240,05 3 4/1941 Richardson. 356/192form white light transmission over the entire compara- 3,529,5l9 9/1970Mitchell 356/191 X tor area and means to facilitate assembly 72.l28.676' 8/1938 lves..; ..4l/6 FOREIGN PATENTS OR APPLICATIONS 20 Cl i15IDj-awing Figures 22,102 ll/l935 Germany 356/194 PATENTEUJUL24 msSHEEI 1 OF 4 um R mww mm M" IWA BYM,% M

PAIENIEBJUL24|975 3.748.045

' sum 2 0r 4 NEUTRAL DENSITY INVENTOR ROfiE/PT H. MITCHELL aym. z.m was.w

ATTORNEYS PAIENIEDJummn SHEEI 3 (IF 4 mvanron 000501 In mrausu avATTORNEYS saw u or 4 hi4 l3 FIG.

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INVENTOR ROBERT w. wraps BY I Zena, ,z A

ATTORNEYS I COLOR COMPARATOR BRIEF SUMMARY OF THE INVENTION comparator.Means are also provided to expedite the manufacture of the comparator.

BACKGROUND OF THE INVENTION The arts of color photography, colorprinting and color processing have grown rapidly in recent years and arenow highly developed. Nevertheless, because of the vagaries of colorprocessing, color reproduction and color dyes, precise reproducibilityof particular colors under varying conditions and with varying rawmaterials has been difficult. Depending upon the quality of reproductionrequired in a given case, highly sophisticated complex and expensiveequipment and procedures have been employed to calibrate light sources,original material, processing chemicals and the like.

To simplify these procedures and adapt to the variations in rawmaterials, various devices have been marketed which will electronicallyenergize light sources and will measure both the optical density and thecolor characteristics of various original material, sensitive materialand the like. These have included simple neutral density diaphanous stepwedges to determine the proper exposure time or light intensity duringprocessing. Alternatively, step wedges of color filter material of agiven known color have been assembled and used in processingto improvethe color rendition in the end product and to compensate for thevariations in. light sensitive paper, original material andlprocessinglight sources and the like. No single device has been providedheretofore which could satisfactorily be employed, bothby theprofessional and the home photography enthusiast to quickly and easilycalibrate the materials, conditions and original negative ortransparency to insure an accurate reproduction.

, OBJECTS OF THE INVENTION It isan object of this invention to provide asimple, accurate and yet inexpensive device which will, when properlyused, accurately indicate the filter compensation to be employed in acamera to provide accurate '45 opaque sheet 28 over substantially itsentire area.

balanced initial transparencies, in an enlarger or repro-- I ducer toprovide color balanced prints or reproductions of the original, inteaching aids, in color display equipment or the like to provide usefulcolor information and optical density information to the user and in anyother equipment where an accurate and graphic multicolor standard isdesired.

THE DRAWINGS For a more complete understanding of this invention,reference will now be made to the accompanying drawings wherein:

FIG. 1 is a plan view of one color comparator incorporating the featuresof this invention;

FIG. 2 is a sectional view of the embodiment of FIG. 1 taken along theline 2-2 of FIG. 1;

FIG. 3 is a second sectional view of the embodiment of FIG. 1 takenalong the line 3-3 of FIG. 1;

FIG. 4 is a diagrammatic illustration of one use of the embodiment ofthis invention illustrated in FIG. 1;

FIG. 5 is a diagrammatic view of an alternate use of 7 this invention asit is exemplified in FIG. 1;

FIG. 6 is an exploded view of the color filter portion of the embodimentof FIG. 1;

FIG. 7 illustrates the step wedge assembly forming a part of FIG. 6 andrepresenting one particular hue or color;

FIG. 8 illustrates one means for compensating the embodiment of FIG. 1to provide substantially uniform white light transmissivity;

FIG. 9 illustrates an alternate embodiment of the color portion of FIG,1 utilizing six different standard hues;

FIG. 10 is an exploded view illustrating the manner in which theembodiment of FIG. 9 is assembled,

FIG. 11 illustrates one means for compensating the embodiment of FIG.9to provide substantially uniform white light transmissivity;

FIG. 12 illustrates diagrammatically one technique for efficientlyassembling the embodiment of FIG.-6;

FIG. 13 illustrates an alternate neutral density device for theembodiment of FIG. 1;

FIG. 14 is a sectional view taken on the line 14-14 of FIG. 13; and

FIG. 15 is a-sectional view of the embodiment of FIG. 13 taken on theline 14l4 thereof.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to the drawings, andmore particularly to FIGS. 1-5, a color comparator 20, comprising oneembodiment of the invention, is shown in FIGS. 1-3 and is shown inposition in a light box 22 in FIG. 4. The comparator is shown in use onthe easel 24 of an enlarger 26 in FIG. 5. The comparator 20 of FIG. 1comprises an opaque, rectangular sheet 28 having cutout portions todefine the hue measuring area 30: The opaque sheet 20 ispreferablybacked with a. transparent flexible sheet" 36 which is sealed to theapertured In the particular embodiment 20 of FIG. 1, a built-up matrix38 of acetate or gelatin filter media isassembled on top of the opaquebase 28 and the matrix is covered over with a transparent film 40. It iscontemplated that one of the films 36 or will be formed fromphotosensitive material which is processed to produce a pattern ofneutral density material as described in greater detail below. Eachmatrix area will have a neutral density which is the complement of thecolor density of that area.

The thicknesses of the various sheets, films andfilter media shown inFIGS. 2 and 3are highly exaggerated for illustrative purposes and itshould be understood that in actual assembly the entire color comparatorutilizing present commercially available acetate filters as an example,would be in the order of one-tenth of an inch. Filter media especiallydesigned for this application will presumably reduce the thickness stillfurther. The various areas of neutral density material and color filtermedia will be secured to the opaque base 20':and the entire assemblywill be sealed as a laminated entity with the edges of the film 40, theedges of the:opaque' base 28 and the edges of the lower film 36 beingsealed together.

In the preferred embodiment of FIG. 1, the matrix 38 is designed tocreate the appearance of an orthogonal projection of a cube-likestructure having six external corners and a central visible corner 46.The central visible corner 46 will be a patch of neutral density mate-'rial having a light transmission density corresponding to the whitelight transmission density of the color filter media at the points wherethat density is a maximum.

In the embodiment of FIG. 1, the matrix 38 is made up of a plurality ofchevron-shaped uniform filter materials 48-56, each of which has theshape illustrated in the exploded view of FIG. 6 and of varying widths.Thus, for example, the chevron-shaped filter media 48-56 of FIG. 6 wouldall be of a single color or hue, such as, for example, magenta. Asimilar set of chevrons would be assembled as shown in FIG. 6 with thebight portion of each chevron pointed downwardly to the lower corner 58of FIG. 6 and all of these could, for example, be cyan. A third set ofsimilar chevron-shaped filter materials would be assembled with thebight portions directed to the upper left-hand corner 60 of the assemblyshown in FIG. 6 and this set of elements could, for example, be yellow.

Thus, referring again to FIG. 1, the corner 60 of the color portion ofthe comparator 20 would be a yellow filter media and the patches lyingalong the line between corner 60 and center 46 would all have a yellowhue of varying density. Similarly, in FIG. 1, the upper right-hand comer62 and all patches lying between the upper right-hand corner 62 and thecenter 46 would have a magenta hue of varying .intensity.

Finally, the lower corner 56 and all areas lying between corner 56 andcenter 46 will have a cyan hue of varying intensity. All other patchesor areas will comprise combinations of any two of the three basic colorsinvolved with the upper corner 64 having a red hue, the lower leftcorner 66 having a green hue and the lowerright corner 68 having a bluehue.

Each of the rows or diagonals extending outwardly from center area 46will reflect increasing color densities. In one preferred embodiment ofthe invention, each of the first four steps reflects an increase of (or.05) of filter density so that the respective steps are 5,

l0, l5 and 20 with the final step at each of the three corners 56, 60and 62 being twice the adjacent step or a color density of 40.

As should be clear from FIG. 6, the chevron-shaped materials each havesmall bight portions which are not covered 'by any other color mediathus defining the center neutral patch 46 and three spokes extending tothe corners 56, 60 and 62 which have thereon only the one colorassociated with the bight portions lying along that spoke. In thepreferred embodiment, there is, of course, additional complementaryneutral density material.

The manner in which the comparator 20 can be used in practice isillustrated in FIGS. 4 and 5. FIG. 4 shows the comparator 20 assembledin an aperture 70 in the light box 22. The light box includes areflective wall 72 which is disposed at 45 to receive impinging lightrays illustrated by arrows 74. The light rays 74 are reflected from thereflective surface of angular wall 72 and transmitted through thecomparator 20. The light may be observed from in front of the light box22 so that the light rays 74 can be optically evaluated by an observer.

If the center area 46 has the proper neutral gray hue, then the observerwould know that the light rays 74 had a neutral or white character andthe proper optical temperature for the particular use contemplated.This, of course, depends upon the precise selection of neutral densityfor the patch 46.

If the observed light through the central patch 46 has a color cast,then the observer can select an alternate area of the matrix which hasthe desired neutral color and either change the light source accordinglyor add filter media in the path of the light rays 74. This can readilybe accomplished because of the nature of the color matrix.

For example, if the particular patch which provides a neutral visualeffect is disposed in the lower righthand quadrant of the matrix, theobserver merely counts the number of squares that the neutral path isbelow the axis 46-62 and to the right of the axis 46-56 and thisimmediately indicates the amount of filter compensation required. If,for example, the comparator 20 is constructed using increments of cyan,yellow and magenta of 5 units of density per set, one would merely countthe number of steps or sets in each of the three orthogonal directions(never more than two of the three, of course) and add the requiredamounts of cyan, yellow and magenta, respectively, to correct the lightto neutral.

Such a light box 22 can also be constructed with a top cover and aninternal light source which may be electrically energized and haveappropriate filters disposed between the light source and the front walland comparator 20. The filters or electrical voltage can then be alteredto make desired compensations in the observed colors or to establish astandard light source. Such a technique is valuable in evaluating lightsources, in evaluating filter materials, in teaching the theory of lightand in various other obvious applications of the equipment.

Furthermore, the light box 22 may be employed for calibrating colorreversal film and the like. A camera I 76 may be disposed in front ofthe box 22 and focused on the front face 78. A test exposure may then betaken with camera 76 and developed in order to calibrate the particularlot of film being employed. If a standard light source has beenemployed, the transparency, when developed, can be viewed and the colorerror in the film observed. By merely placing the proper filter on thecamera based upon the observation, an accurate color correction of colorreversal film can be accomplished.

Another use of the invention is illustrated in FIG. 5. There a piece ofsensitive color paper 78 is disposed on the easel 24 of enlarger 26. Thecomparator 20 is disposed on sensitive paper 78 and exposed to lightrays 80 from the enlarger head 82. A film 84 is preferably disposed inthe negative tray of the enlarger head and the film should be aphotograph of a known neutral gray field so that the light rays 80impinging on comparator 20 will be of the desired neutral character.When the sensitive paper 78 is then developed, the area corresponding tothe central patch 46 should be neutral. If it is not, the proper filtercompensation can be readily determined from the printed matrix andfilters placed in the filter tray 86 of the enlarger.

If the operator does not have a negative of a neutral gray field, anynegative may be employed with a color diffuser such as a frosted glassemployed in the enlarger head, either adjacent to the objected lens orat some other point in the'path of projected light 80.

The chevron-shaped elements of magenta filter material 48-56 haveidentical shapes except that they have a stepped relationship of widthso that when stacked, they appear as shown in FIG. 7 with the uppermostelement 48 overlying the upper edge of element 50 and in a similarmanner elements 48 and 50 overlying the upper edge of element 52,whereby all of the elements 48-56 have a common aligned edge 88. Theelements 50-56 in the embodiment discussed above would each have a colordensity of 5 while the element 48 would have a color density of 20 andthey would all be of an identical magenta hue.

A similar assembly would be made of cyan and yellow media and the cyanand yellow assemblies are already shown in the basic cube at the bottomof FIG. 6.

While the particular densities described above appear to produce optimumresults for most applications, any desired combination may be employed.For example, the steps could be 10, 20, 30, 40 and 80, respectively.Whatever steps are selected, it will be apparent that the transmissivityof white light through the matrix will vary from the center of the cubeto the six corners and will vary at a more rapid rate at the corners 64,66

and 68 where the filter media thicknesses are doubled.

pends upon the desired size and shape of the various areas of color. Itis generally desired that the neutral 7 area 110 be enlarged somewhatfor easier evaluation tral density material is employed in the matrix.One

technique of using a photographic film having the neutral densitypattern was described above. Another technique for incorporating neutraldensity material is shown' in FIG-8. As shown there, any of the steps48-56 of the .step assembly can be combined with a complementary neutraldensity film '94 which, when combined with the step, will fillthe'entire hexagon associated with that step. Thus, asthe step depthincreases, the size of the neutral density complement will 'decrease andas the density of the step increases, the density of the neutral portion94 will also increase cor resp'bndin'gly. A narrow stripof opaquematerial 96 may beincorporated between the step 48 and theneutrarmediu'm 94 which will produce a narrow white line I l in anyprint of the comparator. The use of the narrow band 96 to define eacharea of the matrix is found helprun" performing visual evaluation.

An alternate embodiment of the invention shown in FIGS. 9 and 10incorporates the three subtractive colors, magenta, cyan and yellow, andthe three additive c'olors,red, green and blue, in a single hexagonalconfiguration. The-particular configuration shown has reand theparticular configuration shown servesthis pur-' pose. If desired, eachof the six sets of filter material could define straight lines with thepure material falling at the mid point of each line. Such aconfiguration renders the evaluation and use somewhat more difficult.

The manner in which the five magenta chevrons 98-l06 are assembledtogether and are assembled with the other five sets can be clearly seenfrom the ex plodedview of FIG. 10.

One particularly expedient method of assembly is illustrated in FIG. 12.As shown in FIG. 8, each filter 'material of each set may be providedwith apertures 112 .in such a manner that proper assembly providesalign-' ment of the apertures. The color and neutral density materials48, 94 and the. like are assembled over a set of spaced pins 114 whichare. mounted on a base 116.

As can be seen in the particular embodiment, each color material willhave three apertures and each neutral density material will also havethree apertures and alignment will be assured. Furthermore, one of thetransparent cover films 36 or 46 may be imprinted with the entire matrixof lines 46or produced photographically and also be apertured to providepositive index- As each layer is constructed, the spokes of the neutralmaterial 32 would become wider while the legslof the color materials118, and 122 wouldbecorne narrower. i

' Instead of assembling'the neutral density material in the mannerillustrated in FIG. 8, it is contemplated that the transparent backing36 of FIG/2 can be formedin tegrally with the various neutral densityareas andbe' a photographically produced complementary pattern, apreformed Iamina'teor a molded product. One such configuration is shownin FIGS 13-15,. In the configuration, of FIGS. 13-15, every area'of thecolor matrix 38 has a thickness or neutraldensity corresponding to thecomplement of thecolor filter density and, thus, provides a unique areal'24'-l40,"etc.," or diminishing density from the center outwardly inall directions.

'As shown in FIG. 15, the section through the right hand column of areasshows that the areal42 hasa thickness or density half that of the centerarea 124and each area there below 144-150 has a density or thick.

ness half that of thecorresponding area in the center As will beapparent from the foregoing, this invention provides a novel device forcolorimetry inwhich aisirnple visual inspection of an orthogonalprojection of 'a cube on a planar surfaceor a similar display ofspatially related color areas enablesquick, accurate and'-inexpensivecolor evaluation. By incorporating complementary neutral densitymaterial, the accuracy OfiStIGh' evaluation is greatly enhanced.

fully explain the character of the invention that others may, byapplying current knowledge, readily adapt the same for use under varyingconditions of service, while retaining certain features which mayproperly be said to constitute the essential items of novelty involved,which items are intended to be defined and secured by the followingclaims.

I claim:

1. A color comparator comprising a supporting base defining a centralaperture and a plurality of partially overlapping similarly shapeddiaphanous color elements supported thereon and partially overlying saidaperture, said plurality of color elements including at least one set ofcolor elements, each set including at least one color element of each ofa plurality of different colors with all of the color elements of saidset having substantially the same predetermined color density, eachcolor element having a central portion and two oppositely disposed endportions, all of the color elements in a set being arranged in a singlelogical end-to-end closed pattern with said end portions of saidelements in overlapping relationship to provide predetermined colorcombinations thereof disposed within said central aperture.

2. The color comparator of claim 1 wherein said base and said colorelements are diaphanous.

3. The color comparator of claim 1 wherein neutral density transmissionmeans overlie said color elements between the ends of said colorelements which overlie the corresponding ends of adjacent color elementswhereby the entire comparator has a substantially uniform effectivetransmission density.

4. The color comparator of claim 1 including at least two sets of colorelements each set having a plurality of elements having colorscorresponding to elements in the remaining sets, said sets being in analigned relationship with the corresponding colors thereof alignedside-by side, one of said sets having a color density less than that ofthe adjacent of said sets by a predetermined increment of color density.

5. The color comparator of claim 4 wherein the ends of the elements ofeach of said sets effectively overlap all of the elements of theadjacent sets.

6. The color comparator of claim 4 wherein neutral density transmissionmeans overlies said one set of color elements whereby said one set andsaid adjacent set of color elements have'a substantially equal effectivetransmission .density.

7. The color comparator of claim 1 wherein said set comprises threecolor elements.

8. The color comparator of claim 7 wherein the colors of said colorelements are cyan, magenta and yellow.

9. The color comparator of cliam 7 wherein the colors of said colorelements are red, blue and green.

10. The color comparator of claim 1 wherein said set comprises six colorelements.

11. The color comparator of claim 10 wherein the colors of said colorelements are cyan, magenta, yellow, blue, green and red.

12. The color comparator of claim 1 wherein each of said color elementsis an elongate element having two end portions disposed at an obtuseangle and a bight portion.

13. The color comparator of claim 5 wherein each of said sets comprisescolor elements of cyan, magenta and yellow.

14. The color comparator of claim 11 wherein each of said color elementsis an elongate element having two leg portions disposed at an acuteangle and a bight portion, the end portions overlying end portions ofadjacent elements in the sequence: blue, cyan, green, yellow, red andmagenta.

15. The color comparator of claim 14 wherein said overlying ends extendoutwardly and said bight portions extend inwardly to define asix-pointed star and the center of said comparator has a neutraldensity, neutral density material overlying each intersection of twoelements except the outer-most intersection at each point of the starand overlying said center to provide substantially uniform transmissionof white light over the area of said comparator.

16. The color comparator of claim 5 wherein each of said color elementsis formed of filter material having an area corresponding to the area ofsaid element and an appropriate transmissive density and hue, saidmaterial being assembled in a generally planar arrangement on said baseto provide the desired hues in each overlapping area of said elements. 7

l7. Thecolor comparator of claim 5 comprising a plurality of pieces ofcolor filter material, one piece corresponding to each color of eachset, the area of each piece of a given set being the area of thecorresponding color element of the set plus the area of the colorelements of the corresponding color of each set having a color densitygreater than said given set and the color density of said piece beingequal tothe color density corresponding to said given set reduced by thecolor density of all less dense sets.

18. The color comparator of claim 17 including a plurality of sets, eachhaving an increase of color density from the inner adjacent'set, allofsaid increases being equal, and an outermost set having a color densitytwice that of the adjacent set.

19. A diaphanous color comparator comprising a supporting base defininga central aperture and a plurality of partially overlapping similarlyshaped diaphanous color elements supported thereon and partiallyoverlying said aperture, said plurality of color elements including atleast two sets of color elements, each set having a plurality ofelements having different colorsand corresponding in color tocorresponding elements in the remaining sets, said sets being in analigned-relationship with the elements having corresponding colorsthereof aligned, and all of the color elements of any set havingsubstantially the same color density, each of said color elements havingtwo elongate leg portions and a bight portion, the elements of each setbeing arranged in a single logical, end-to-end closed pattern with legportions in'overlapping relationship, each set of elements having acolor' density less than the adjacent set and theoutermost sethaving thegreatest color density whereby the visual effect created by saidcomparator is that of a single diaphanous geometric pattern of aplurality ,of different colors disposed about the periphery of saidaperture in said base and a plurality of different color densities ofincreasing magnitude extending outwardly from the central portion of thecomparator and inwardly from the periphery of said aperture.

20. The color comparator of claim 19 wherein said leg portions aredisposed at about relative to one another and each of said sets includesthree elements of different colors, the elements being arranged toproduce a visual effect of an orthographic projection with a neutraldensity appearing centrally in the comparator.

i i t I?

1. A color comparator comprising a supporting base and a plurality ofpartially overlapping similarly shaped color elements supported thereon,said plurality of color elements including at least one set of colorelements, each set including at least one color element of each of aplurality of different colors with all of the color elements of said sethaving substantially the same predetermined color density, each colorelement having a central portion and two oppositely disposed endportions, all of the color elements in a set being arranged in a singlelogical end-to-end closed pattern with said end portions of saidelements in overlapping relationship to provide predetermined colorcombinations thereof.
 2. The color comparator of claim 1 wherein saidbase and said color elements are diaphanous.
 3. The color comparator ofclaim 1 wherein neutral density transmission means overlie said colorelements between the ends of said color elements which overlie thecorresponding ends of adjacent color elements whereby the entirecomparator has a substantially uniform effective transmission density.4. The color comparator of claim 1 including at least two sets of colorelements each set having a plurality of elements having colorscorresponding to elements in the remaining sets, said sets being in analigned relationship with the corresponding colors thereof alignedside-by-side, one of said sets having a color density less than that ofthe adjacent of said sets by a predetermined increment of color density.5. The color comparator of claim 4 wherein the ends of the elements ofeach of said sets effectively overlap all of the elements of theadjacent sets.
 6. The color comparator of claim 4 wherein neutraldensity transmission means overlies said one set of color elementswhereby said one set and said adjacent set of color elements have asubstantially equal effective transmission density.
 7. The colorcomparator of claim 1 wherein said set comprises three color elements.8. The color comparator of claim 7 wherein the colors of said colorelements are cyan, magenta and yellow.
 9. The color comparator of cliam7 wherein the colors of said color elements are red, blue and green. 10.The color comparator of claim 1 wherein said set comprises six colorelements.
 11. The color comparator of claim 10 wherein the colors ofsaid color elements are cyan, magenta, yellow, blue, green and red. 12.The color comparator of claim 1 wherein each of said color elements isan elongate element having two end portions disposed at an obtuse angleand a bight portion.
 13. The color comparator of claim 5 wherein each ofsaid sets comprises color elements of cyan, magenta and yellow.
 14. Thecolor comparator of claim 11 wherein each of said color elements is anelongate element having two leg portions disposed at an acute angle anda bight portion, the end portions overlying end portions of adjacentelements in the sequence: blue, cyan, green, yellow, red and magenta.15. The color comparator of claim 14 wherein said overlying ends extendoutwardly and said bight portions extend inwardly to define asix-pointed star and the center of said comparator has a neutraldensity, neutral density material overlying each intersection of twoelements except the outermost intersection at each point of the star andoverlying said center to provide substantially uniform transmission ofwhite light over the area of said comparator.
 16. The color comparatorof claim 5 wherein each of said color elements is formed of filtermaterial having an area corresponding to the area of said element and anappropriate transmissive density and hue, said material being assembledin a generally planar arrangement on said base to provide the desiredhues in each overlapping area of said elements.
 17. The color comparatorof claim 5 comprising a plurality of pieces of color filter material,one piece corresponding to each color of each set, the area of eachpiece of a given set being the area of the corresponding color elementof the set plus the area of the color elements of the correspondingcolor of each set having a color density greater than said given set andthe color density of said piece being equal to the color densitycorresponding to said given set reduced by the color density of all lessdense sets.
 18. The color comparator of claim 17 including a pluralityof sets, each having an increase of color density from the inneradjacent set, all of said increases being equal, and an outermost sethaving a color density twice that of the adjacent set.
 19. The colorcomparator of claim 1 wherein said base is apertured and said colorelements overlie the aperture in said base.
 20. The color comparator ofclaim 1 wherein said color elements are diaphanous.
 21. A colorcomparator comprising a supporting base and a plurality of partiallyoverlapping similarly shaped color elements supported thereon, saidplurality of color elements including at least two sets of colorelements, each set having a plurality of elements having differentcolors and corresponding in color to corresponding elements in theremaining sets, said sets being in an aligned relationship with theelements having corresponding colors thereof aligned, and all of thecolor elements of any set having substantially the same color density,each of said color elements having two elongate leg portions and a bightportion, the elements of each set being arranged in a single logical,end-to-end closed pattern with leg portions in overlapping relationship,each set of elements having a color density less than the adjacent setand the outermost set having the greatest color density whereby thevisual effect created by said comparator is that of a single geometricpattern of a plurality of different colors disposed about the peripheryof said comparator and a plurality of different color densities ofincreasing magnitude extending outwardly from the central portion of thecomparator.
 22. The color comparator of claim 21 wherein said legportions are disposed at about 120* relative to one another and each ofsaid sets includes three elements of different colors, the elementsbeing arranged to produce a visual effect of an orthographic projectionwith a neutral density appearing ceNtrally in the comparator.